Magnetic materials are roughly classified as a hard magnetic material and soft magnetic material, and when both materials are compared, a high coercivity is required of the hard magnetic material, whereas high maximum magnetization is required of the soft magnetic material, though the coercivity may be small.
The coercivity characteristic of the hard magnetic material is a property related to the stability of magnet, and as the coercivity increases higher, the magnet can be used at a higher temperature.
One known magnet using a hard magnetic material is an NdFeB-based magnet which can contain a microcrystalline texture. It is also known that a high-coercivity quenched ribbon containing the microcrystalline texture can be improved in the temperature characteristics and thereby improved in the high-temperature coercivity. However, the coercivity of the NdFeB-based magnet containing a microcrystalline texture decreases during sintering at the bulking as well as during orientation control after sintering.
With respect to this NdFeB-based magnet, various proposals have been made so as to improve characteristics such as coercivity and residual magnetic flux density.
For example, in Patent Document 1, a permanent magnet in which an R—Fe—B-based alloy (R is a rare earth element including Y) prepared through melting and quenching is imparted with magnetic anisotropy by plastic working and in which the average crystal grain size is from 0.1 to 0.5 μm and the volume percentage of a crystal grain having a crystal grain size of more than 0.7 μm is less than 20%, is described and it is demonstrated that in the case where the average crystal grain size after plastic working is less than 0.1 μm, anisotropic orientation of crystal grains does not proceed sufficiently. Furthermore, as a specific example of the production method, a case of obtaining a rare earth magnet through thinning by quenching of a molten alloy, cold forming, hot pressing, and anisotropic orientation by plastic working is described.
Also, in Patent Document 2, a production method of a rare earth permanent magnet is described, wherein a sintered body with a composition of Ra-T1b-Bc (wherein R is one element or two or more elements selected from rare earth elements including Y and Sc, T1 is one or two members of Fe and Co, and each of a, b and c represents an atomic percentage) is heat-treated while allowing an alloy powder having a composition of M1d-M2e (wherein each of M1 and M2 is one element or two or more elements selected from Al, Si, C, P, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb and B1, M1 and M2 are different from each other, and each of d and e represents an atomic percentage) and containing 70 vol % or more of an intermetallic compound phase to be present on the surface of the sintered body, at a temperature not more than the sintering temperature of the sintered body in vacuum or in an inert gas and thereby, one element or two or more elements of M1 and M2 contained in the powder are diffused near the grain boundary part inside of the sintered body and/or the grain boundary part in the main phase grain of the sintered body.